What Magnesium Actually Does for Horses

Magnesium seems to be a standout ingredient in horse supplements right now. From calmers to behavioural support, magnesium is everywhere! But what does magnesium actually do, and how could it benefit your horse?

What is Magnesium?

Magnesium is an essential macromineral, which simply means that horses need it in their diet in relatively large amounts to support normal body function.

Around 50–60% of magnesium is stored in the skeleton, most of the rest is found in muscles and soft tissue, and less than 1% circulates in the blood. Magnesium is involved in hundreds of cellular processes within the body, with standout roles in energy production and neuromuscular function.

Energy

Magnesium binds to ATP, the body’s energy currency, to form a complex called Mg-ATP. This complex is used by enzymes to power numerous processes within the body, including muscle contraction, nutrient metabolism and nerve signalling.

Muscles

Muscles work by contracting and relaxing their fibres. Calcium, another essential macromineral, triggers muscle fibres to contract, whilst magnesium helps regulate calcium activity and the processes that allow muscles to relax again.

Nerves

Your horse’s nervous system relies on nerve cells sending and receiving signals in a carefully controlled way. Magnesium helps keep that activity in a ‘Goldilocks’ zone: neither too overactive nor too underactive, supporting normal nerve signalling.

Alongside these essential functions, magnesium also supports the formation of strong, healthy bones, helps maintain electrolyte balance and contributes to cardiac stability, helping to prevent irregular heartbeats. A real all-rounder!

How Do Horses Get Magnesium?

‘If magnesium is so important, surely horses must get enough of it from their diets?’

Yes (and no)! Horses can’t make magnesium themselves, so it has to come from what they eat. Forage provides most of it, and feeds like alfalfa, sugar beet and wheat bran are also rich in magnesium. As a rough guide, the National Research Council (NRC, 2007) estimates that a 500 kg adult horse requires around 7.5 g of magnesium per day at maintenance. This increases to approximately 9.5 g for light exercise, 11.5 g for moderate exercise and 15 g for heavy or very heavy exercise. Growing horses and lactating mares have different requirements, depending on their age and stage of lactation. These figures refer to the horse’s total daily magnesium intake from forage, feed and supplements combined.

However, how much magnesium a horse can consume and actually absorb can vary. Magnesium can be difficult to absorb in the gut, and feeds high in other nutrients, such as calcium, can make absorption even harder. Other factors that can limit uptake include:

·      Soil and forage quality Many UK soils are naturally low in magnesium, and levels vary with region, season and how forage is grown and stored.

·      Fast-growing grass Lush Spring and autumn grass is often high in potassium, which can reduce magnesium absorption.

·      Workload and travel Horses lose water and electrolytes, including magnesium, through sweat. Those working hard, travelling or competing, particularly in hot weather, may need additional electrolyte support. The highly palatable Apple Lytes Granules provide a balanced blend of key electrolytes, including sodium, potassium, chloride, calcium and magnesium, to help replace losses and support rehydration.

·      Life stage Magnesium requirements vary with a horse’s age and physiological stage. Growing horses and lactating mares have different nutritional requirements from mature horses at maintenance, so their overall diets should be assessed accordingly.

·      Limited forage Sparse winter pasture or low-forage diets can mean lower intake.

Could My Horse Be Low in Magnesium?

Low blood magnesium (hypomagnesaemia) can occur in horses with gastrointestinal issues. Soil mineral levels vary, and nutrient losses through leaching can affect the mineral content of the grass and forage grown on it. As forage is a major source of magnesium for horses, intake can vary depending on its quality and how much they eat. Others may simply show signs such as:

·      Muscle tension, twitching or tremors

·      Stiffness or slow recovery after work

·      Sensitivity to touch or reluctance to be groomed

·      Spookiness, nervousness or difficulty settling

·      Lethargy or reduced appetite

“My Horse Is Spooky. Do They Need Magnesium?”

It’s one of the most common questions asked, and for good reason!

Spookiness alone doesn’t necessarily mean your horse needs more magnesium, as behaviour can be influenced by many factors. As mentioned earlier, forage is a key source of magnesium, but its nutritional content can vary depending on soil, growing conditions and forage type. Many horses therefore receive a vitamin and mineral supplement or a vitamin- and mineral-inclusive balancer to help meet their daily nutritional requirements.

If you have concerns about low magnesium, look no further than Magnitude, which provides a concentrated source of magnesium from magnesium oxide, helping to supplement the diet where magnesium intake may be marginal.

If you’re still unsure what your horse needs, why don’t you get in touch with our friendly team of nutritionists and vets at vet@equine-america.co.uk

Magnesium, Stress & Calming

Horses evolved as prey animals with finely tuned fight-or-flight responses. Whilst these responses originally evolved to protect against predators, modern-day stressors like travel, competition, intense exercise, isolation and cold can all trigger the release of stress hormones, such as adrenaline and cortisol, which can lead to nervous, spooky behaviour.

So Where Does Magnesium Fit In?

When horses encounter a stressful situation, their nervous system becomes more active, triggering the release of stress hormones such as adrenaline and preparing the body to react.

Inside the body, magnesium and calcium work together to regulate nerve activity. Calcium helps activate nerve cells and triggers the release of chemical messengers, including those involved in the stress response, such as adrenaline. Magnesium has the opposite effect, helping to regulate calcium activity and nerve cell excitability, preventing overstimulation and helping reduce the stress response.

How to Choose a Calmer

Not all magnesium supplements are made alike! When comparing them, look at the source of magnesium, how easily it can be absorbed and what else is included to support calming and behaviour.

So-Kalm and Super So-Kalm combine bioavailable magnesium with vitamin B1, which contributes to normal nervous system function, and L-tryptophan, an amino acid horses use to make serotonin. Together, they provide broader nutritional support to help maintain a calm outlook and concentration.

For horses needing short-term support for situations such as travelling, competition or new environments, why not try So-Kalm Paste or Super So-Kalm Paste for easy feeding and happy adventures?

Magnesium: The Takeaway

Magnesium is a hugely important mineral for horses, with key roles in energy, muscle and nerve function. It’s a popular ingredient in many calming and behavioural supplements, so look for the right form and the right ratios to ensure a balanced approach to calming.

For more information, please contact our technical team, which includes qualified and registered nutritionists and veterinary surgeons.

Sources

·      Quattrini, C. (2026) ‘Magnesium dysregulation’, Veterinary Clinics of North America: Equine Practice, 42(3)

·      Noble, J. (2012) ‘Magnesium — a wonder supplement?’, Equine Health, 2012(7)

·      Budzyńska, M. (2014) ‘Stress reactivity and coping in horse adaptation to environment’, Journal of Equine Veterinary Science, 34(8)

·      Hollands, T. and Drury, L. (2023) Evidence-Based Equine Nutrition: A Practical Approach for Professionals. 1st edn. CAB International.

·      Geor, R.J., Harris, P.A. and Coenen, M. (eds.) (2013) Equine Applied and Clinical Nutrition: Health, Welfare and Performance. Edinburgh: Saunders Elsevier.